1. Field of the Invention
The present invention relates generally to a Pyroelectric Infrared Sensor (hereinafter described as an infrared sensor). More particularly, this invention relates to several undermentioned improvements and developments of the adhesion between a can and window material, the adjustment of the electromotive force from the sensing elements, the dimensions and the electric connection of the sensing elements, the adaptability among the sensing elements and other peripheral components or parts, and the supplemented optical material for use mainly in an intrusion alarm system.
2. Description of Relevant Art
Generally in many known infrared sensors, a window material such as Si, Ge or Al.sub.2 O.sub.3, etc., is adhered to a can. The window material is able to transmit infrared energy and has a conductivity that results either from an inherent characteristic of the material itself or from appendant processing. Further such window material must be adhered to a can in the conductive state.
It is well known that sensing elements having a concentric-circle shape are most suitable for infrared sensors which are mounted and installed on higher portions such as the ceiling, etc., and that plural sensing elements for each identical sensing electrode area are preferred for the above-mentioned applications.
It is apparent that placement of a pair of sensing electrodes on a substrate is an efficient production process. It is also desirable that a pair of sensing elements and their peripheral components be symmetrically matched with another pair of sensing elements having similar characteristics. In addition, it is also well known that a costly crescent-shaped negative-meniscus lens, with antireflection coating, consisting of SiO may be assembled or mounted on the infrared sensor in the manufacturing process.
However, the previously known adhesion of a point only between a can and a window using conductive adhesives has some defects resulting from the incomplete conductive adhesion as well as from the non-hermeticity of the seal between the can and the window. Also, infrared sensors for upper or higher portion installation having sensing elements with concentric circle shapes and identical sensing electrode areas, have a serious fault in that they give a false alarm signal dependent upon a change of the ambient temperature, due to the impossibility of perfect temperature compensation.
The infrared sensor includes a can containing two pairs of sensing elements comprising the essential material and having identical characteristics, and peripheral components. The peripheral components can get separate signals from each pair of sensing elements, but even if these independent signals were processed through AND circuitry, false alarms caused by synchronous White Noise or Spike Noise from each sensing element would not be avoidable. And further, conventional infrared sensors having a costly optical member for condensing or adjustment of the optical beam are extremely wasteful because of component failures and poor production yields.
The present invention is intended to improve the reliability and the sensitivity of a wall mounted infrared sensor for an intrusion alarm system.